Short-wave oscillator



Patented Oct. 29, 1929 UNITED STATES ABRAHAM ESAU, OF JENA, GERMANYSHORT-WAVE Application filed October 25, 1927, Serial No.

The present invention relates to the generation of short electric wavesby means of a spark oscillator. \Vhilst formerly very short waves of thedamped kind were generated by means of spark gaps, at the present timethermionic valves are used almost exclusively; these, as is well known,enable undamped oscillations to be produced, such as have gradually comemore and more to the front during the development of the wirelessindustry.

The present invention provides a means for producing waves which arepractically as little damped as possible, with the use of a spark gap,this method, compared with production by means of valves, having anumber of advantages, more particularly when. it is a question of thegeneration of very short waves for large amounts of energy and of goodmodulation.

As is well known, the output obtained in a spark transmitter can beexpressed by the formula VV= z0l in which .2 is the number of sparks persecond, C the capacity of 2. the circuit and V the voltage across thecondenser at the beginning of the discharge. An increase of capacityfor. the purpose of obtaining greater energy output, when it is aquestion of the generation of short waves,

may he at once eliminated, as the wave length Varies with the capacityand the latter must he therefore kept as low as possible. A limit isalso soon set to an increase of voltage and the consequently requiredincrease of the spark gap or of the number of spark gaps firstly becausefor practical reasons the voltage can be raised only up to a certainpoint and further because the electric inherent dimensions of thecircuit increase with the in- 49 crease of the spark gap, and this willagain affect the wave length, respecting which the circuit dimensionsare of paramount importance, more particularly in the case of very shortwaves; thus, an increase of energy cannot be obtained in that manner. Aswill be seen from the formula, there remains only the possibility ofincrease in the number of sparks per second 2. A process has beenalready proposed in which two spark gaps are 5Q connected in cascade andin which the damped OSCILLATOR 228,526, and in Germany October 29, 1926.

oscillations generated by the first spark gap are used for working thesecond spark gap. The oscillations thus obtained are damped,

in the same way as when a single spark gap is used, for the currentsfeeding the second 65 spark gaps are already constituted by dampedalternating current trains succeeding each other. It has also beenproposed to supply spark gaps with low or medium frequency alternatingcurrent up to 2000 periods per second, for the purpose of obtaining anaudible sound in a receiver, that is to say intentionally a dampedoscillation.

According to the present invention a circuit including a spark gap issupplied with alternating current of a frequency higher than that ofaudition, whereby the wave trains generated and following each other, although individually damped, produce a practically undamped oscillation.It is preferable to dimension the spark gap in such a manner that ateach half period of the supply high frequency current, a spark shallpass, producing a corresponding impulse in the oscillation circuit.

For the purpose of generating the alternating current any device knownper se can be used, such as high frequency alternating current machineswhich as a rule give frequencies of about 8000-15000, or voltaic arcs orvalve generators, etc. Further, in the pres.- ent state of the wirelessindustry, there is no difficulty in arranging quenched spark gaps withan action practically suflicient for quenching such high sparkfrequencies as are in question.

The invention will'now be explained more fully with reference to theaccompanying drawing, which illustrates one manner of carrying it intoeffect, and in which:

Figure l is a diagrammatic view of an oscillation system for carrying myinvention into practical efiect.

Figure 2 is a View showing unmodulated and modulated voltages.

Referring to Figure 1, I is the high frequency generating circuit,constituted in the present case by a three electrode valve inoscillation generating connection; for this purpose also a highfrequency machine could 100 be used. II is the spark gap circuit and IIIa work or radiation (aerial) circuit. 1' is the valve, L C arerespectively the valve oscillation circuit inductance and oscillationcircuit capacity, L is a coupling coil for coupling to the spark gap F.C and L constitute the oscillation circuit excited intermittently by thespark gap; the constants of this circuit, when it is a question ofgeneration of very short waves (of the order of value of a few meters orcentimeters) can-be determined by the geometrical dimensions. L is thecoupling coil of the aerial A, and E the point of connection for theearth conductor.

An advantage of the invention is that it is possible to effect in asimple manner a modulation of the waves radiated, for, as is well known,such modulation in the case of short waves offers in practice withpresent systems great difficulties owing to the inconstancy of the wavelengths when using valve generators. For that reason, according to theinvention, the high frequency current used for charging the spark gap ismodulated rather than the oscillations generated (i. e. in Figure 1 theoscillations in the aerial circuit A, L, E) this is efl'ected by aninserted modulation device of'a kind well known in itself, marked M inFigure 1, for example, a microphone or its equivalent. It is anessential condition that the modulation should take place in such amanner that at least the elfective voltage for the spark gap shall bestill retained even in the case of the strongest modulation. This ismore fully shown in Figure 2, in which a indicates the unmodulated highfrequency voltage for the spark gap, 6 the corresponding modulatedvoltage V, Whilst V is the voltage required to produce sparking, that isthe minimum voltage, in the case of the strongest modulation, which mustbe produced.

The invention ofi'ers particularly great advantages when applied to thegeneration of very short waves, not exceeding 1 meter, where a directgeneration, for instance by means of valves, presents greatdifficulties. In'practice, a valve will be utilized for generating theshortest wave which can be adequately generated, and further reductionwill be effected by the connection to a spark gap, owing to which itwill become possible to produce waves of the shortest wave lengths suchas have been hitherto unattained.

What I claim is:

1. A short wave oscillator comprising a vacuum tube generator forproducing undamped high frequency oscillations in a range aboveaudibility range, a spark gap circuit for raising said undamped highfrequency oscillations to a frequency higher than their generatedfrequency, and a work circuit on which the resulting individually dampedsuccessive oscillations are impressed so as to produce a practicallyundamped wave.

2. A short wave oscillator comprising means for producing undamped highfrequency oscillations in a range above audibility range, a spark gapcircuit for raising said undamped high frequency oscillations to afrequency above their generated frequency, a work circuit on which theresulting successive individually damped oscillations are impressed soas to produce a practically undamped wave, and means for modulating saidundamped high frequency currents supplied to the spark gap in accordancewith signals to be transmitted.

In testimony whereof I have afiixed my signature.

ABRAHAM ESAU. 7

